I am a computer engineer but my friend and I are trying to build audio devices, right now we're trying to figure out a device that would take multiple 5v audio inputs and pass through only the signal which is loudest at any given point. Anyone have any ideas on where to start?

Several inputs of the same voltage and you want a circuit to find the one with the highest voltage? You're going to have to continue describing what you want.

Do you want the channel checker to decide every 50 microseconds (1/20,000 Hz) and pass the highest voltage while turning off all the other channels? Make an envelope follower that rides the highest voltage so several channels combine to provide the output? Do a priority over-ride where the priority channel is the highest signal that existed in the last one second?

How frequently do you want to determine which is the loudest (ignoring the fact that they are all stated to be '5V')? If you switch between channels rapidly the result will sound dreadful. Or aren't you interested in sound quality?